Someone's watching your film downloads

Illegally downloading a single blockbuster film or hit song using "torrent" software means your computer is likely to be secretly logged and monitored by copyright enforcement agencies, undercover research has shown.

The digital details of filesharers using websites such as Pirate Bay are monitored within three hours of downloading popular films, music, e-books or software programs, having their computer's IP address stored as "first-hand evidence", according to a three-year study by the University of Birmingham.

Obtaining a pirate version of the latest Batman film is far more likely to result in your computer activity being spied on than hunting down an obscure Italian post-modernist arthouse title.

The study, led by Dr Tom Chothia, found that "monitoring is prevalent for popular content" but absent for less popular content.

Users of BitTorrent, a peer-to-peer file-sharing system that enables people to download files in fragments from "swarms" of multiple users rather than directly from one source, may have been monitored for as long as three years.

A team of computer scientists made the discovery by building their own software that tracked all the connections that were made to it.

Ten monitoring companies were identified by the research, but it is unclear what they do - or plan to do - with the information. There has been speculation the details may be stored in anticipation of a new and more intense crackdown on filesharers in the courts.

However, the paper noted that "direct monitoring, in its current form, falls short of providing conclusive evidence of copyright infringement".

Some of the monitoring may also be carried out simply for research into the extent of filesharing.

If one download is enough to attract a monitoring firm to the culprit's details, the sheer number of filesharers whose internet activity has attracted their attention will be huge.